Active studies have been conducted on providing high-speed services with different Quality of Service (QoS) requirements to users in future-generation communication systems. A major future future-generation communication system is Institute of Electrical and Electronics Engineers (IEEE) 802.16e.
Depending on whether a transmitter (e.g., a base station) receives feedback information from a receiver (e.g., a mobile station), power control schemes are classified into open-loop power control and closed-loop power control in communication systems.
Open-loop power control is a power control scheme in which the transmitter decides on the channel status of the receiver independently without receiving feedback information (for example, channel quality information) and controls power accordingly. The open-loop power control scheme is based on the reciprocity of downlink and uplink channels. The channel reciprocity means that the downlink and uplink channels experience similar path attenuation between the transmitter and the receiver. That is, the open-loop power control scheme is a transmission scheme in which the transmitter itself estimates the signal reception quality of the receiver based on the reciprocity between the downlink and uplink channels, calculates a required transmit power based on the estimation, and transmits a signal with the transmit power.
Closed-loop power control is a power control scheme in which the transmitter controls transmit power based on channel information received from the receiver on a feedback channel without determining the channel quality independently, as compared to the open-loop power control. Despite the shortcoming of overhead from the feedback channel, the closed-loop power control scheme can control the power of a transmission signal more accurately than the open-loop power control scheme since the transmitter gets knowledge of the channel quality of the receiver.
Meanwhile, the future-generation communication system adopts a multi-hop relay scheme in order to enable high-speed communications and accommodate a larger number of calls. Since communications are conducted between a fixed base station (BS) and a mobile station (MS) via a direct link, a highly reliable radio communication link can be easily established between them. However, due to the fixedness of the base station, the configuration of a wireless network is less flexible, making it difficult to provide an efficient communication service in a radio environment characterized by a fluctuating change in traffic distribution and required calls. To avert this problem, the communication system employs a multi-hop relay scheme using fixed or mobile relay stations. The multi-hop communication system can reconfigure a network fast according to an environmental change and operate the entire wireless network efficiently. Therefore, a self-configurable radio network can be implemented in the communication system, taking the form of a multi-hop communication system.
The multi-hop communication system expands cell coverage and increases system capacity by multiple hops. When the channel status between a base station and a mobile station is poor, a multi-hop relay path established with the mobile station via relay stations and thus a better radio channel can be provided to the mobile station. Hence, the use of multiple hops enables provisioning of a more efficient communication service to mobile stations in a shadowing area experiencing severe shielding due to buildings. Also, the multi-hop relay scheme provides a high-speed data channel to a mobile station at a cell boundary in a poor channel status and expands cell coverage.
For the base station to transmit data to the mobile station via a relay station (RS) in a multi-hop relay path, a data transmission power control scheme is required for the base station and the relay station. That is, there exists a need for a transmission power control scheme that efficiently utilizes limited channels, for example, a channel between the base station and the RS and a channel between the relay station and the mobile station, and increases data rates in the multi-hop communication system.